Relationship between spatial distribution of the Patagonian stock of Argentine anchovy, Engraulis anchoita, and sea temperatures during late spring to early summer

The relative abundance of adult Argentine anchovies (Engraulis anchoita) an d the thermal structure of the sea between 41 degrees and 45 degrees 30'S d uring four research surveys were compared. Acoustic data were collected whi le making parallel transects along which CTD (conductivity, temperature, de pth) stations were regularly distributed. Anchovy abundance was related to both the sea surface temperature and the stratification of the water column , as classified according to the phi parameter of stability (Simpson, 1981) . Regarding the whole water column, the sea temperatures where adult anchov ies were recorded ranged from 8.5 to 16.5 degreesC, but anchovy echo traces from waters above 14 degreesC were obtained mainly at night. The sea surfa ce temperature bounds for anchovy distribution were 11 and 17 degreesC, wit h a preferential range between 12.5 and 16 degreesC, but no absolute value of sea surface temperature was found to be most favourable for the species. The highest fish abundances were related to sharp thermal gradients, eithe r horizontally recorded in frontal zones (approximate to 0.02 degreesC or m ore per km) or vertically associated to the occurrence of a thermocline (st ability > 10 J m(-3)). Sea fronts seemed to be the axes for the distributio n of anchovy shoals, and the annual changes in the positions of the fronts seemed to be followed by analogous changes in the locations of the main anc hovy concentrations. Within thermally stratified areas and during the dayti me, anchovies apparently preferred the thermocline layer or the layer immed iately above that, although a few fish shoals were located below the thermo cline.